1. Field of the Invention
This invention relates in general to digital signal processing, and more particularly to a customer premises equipment (CPE) alert signal tone detector.
2. Description of Related Art
In the field of electronics, accurate data transfer over telephone lines has become one of the greatest demands on any data system. The problems of discerning a proper data incoming tone, false signal recognition, and ensuring that data is not lost during noisy transmission have been challenges for engineers to overcome.
Customer premises equipment (CPE) can take many forms, e.g., facsimile machines, computer modems, or other telephone interface equipment.
Further, new features offered by telephone service providers, such as caller ID, caller ID with call waiting, and Analog Display Services Interface (ADSI) require that a telephone switch transmit and receive digital data and voice signals over the same standard analog phone connection, making the detection of a specific tone even more difficult.
The first and largest problem that this class of data transfer system faces is how to determine whether there is data coming in.
It can be seen, then, that there is a need for a system that can alert the CPE when there is incoming data. It can also be seen that the CPE alert system must work under a variety of conditions.
To minimize the limitations in the prior art described above, and to minimize other limitations that will become apparent upon reading and understanding the present specification, the present invention discloses a method, apparatus, and article of manufacture for detecting a Customer Premises Equipment (CPE) alert signal (CAS) tone.
The present invention solves the above-described problems by measuring various characteristics of the incoming signal to determine if the signal is a CPE alert tone.
A method in accordance with the principles of the present invention comprises measuring an RMS level, a twist, a side band, and a frequency of an incoming signal and storing the measurements in a memory of a computer, verifying that the RMS level of the incoming signal exceeds a threshold, verifying that the RMS level of the incoming signal exceeds that of a level of the side band of the incoming signal, verifying that the twist of the incoming signal does not exceed a given value, verifying that the frequency of the incoming signal is within a percentage of a nominal value for the incoming signal, and enabling continued receipt of an incoming signal to the memory of the computer based on the verification of the RMS level, the verification of the twist, and the verification of the frequency of the signal.
These and various other advantages and features of novelty which characterize the invention are pointed out with particularity in the claims annexed hereto and form a part hereof. However, for a better understanding of the invention, its advantages, and the objects obtained by its use, reference should be made to the drawings which form a further part hereof, and to accompanying descriptive matter, in which there is illustrated and described specific examples of an apparatus in accordance with the invention.